I think Lemmy has a problem with history in general, since most people on here have degrees/training in STEM. I see a lot of inaccurate “pop history” shared on here, and a lack of understanding of historiography/how historians analyze primary sources.
The rejection of Jesus’s historicity seems to be accepting C S Lewis’s argument - that if he existed, he was a “lunatic, liar, or lord,” instead of realizing that there was nothing unusual about a messianic Jewish troublemaker in Judea during the early Roman Empire.
This passage in Josephus’s Antiquities would be the best evidence outside of the New Testament texts. Josephus refers to “Jesus, who was called Christ”’s brother James being executed, likely due to his role in leading an early group of Christians.
You can also read Bart Ehrman for some analysis and arguments from a professional historian.